Liquid crystal displays (LCDs) are optical displays used in devices such as laptop computers, hand-held calculators and digital watches. A typical LCD includes an LCD layer and an electrode matrix, disposed between a pair of absorbing polarizers. For color displays, the LCD typically also includes a color filter. The optical state of portions of the LCD cell is altered by the application of an electric field using the electrode matrix. The combination of the altered optical state of the liquid crystals and the polarizers results in the appearance of pixels of polarized light on the liquid crystal display to form the desired image.
A typical liquid crystal display includes a front polarizer, closer to the viewer, and a rear polarizer, on the other side of the LCD from the viewer. These polarizers are plane polarizers that absorb light of one polarization orientation more strongly than light of the orthogonal polarization orientation. The transmission axis of the front polarizer is usually crossed with respect to the transmission axis of the rear polarizer in a liquid crystal display.
Much commercial attention has been directed to the development and improvement of flat panel displays, particularly thin, compact flat panel displays. A problem encountered in the construction of plastic flat panel displays is the development of “black spots,” which arise from the formation of bubbles in the liquid crystal material from gas that has permeated through the plastic display materials. Another problem associated with plastic flat panel displays is moisture contamination of the liquid crystal display cell. These problems are avoided in conventional liquid crystal displays by using low permeability glass substrates instead of plastic. With respect to plastic flat panel displays, these problems are addressed by adding additional gas and moisture barrier layers to the liquid crystal display structure and/or the plastic substrates. However, adding such gas and moisture barrier layers increases the thickness, weight and cost of the displays.
Polarizers in the form of synthetic polarizing films exhibit comparative ease of manufacture and handling. In general, absorption polarizing films preferentially absorb light having its electric vector directed along one direction, referred to as the absorption polarization state, and transmit light polarized orthogonal to the absorption polarization state, referred to as the transmission polarization state. This property is referred to as dichroism.
Absorption polarizers include H-type (iodine) polarizers and dyestuff polarizers. An H-type polarizer, for example, is a synthetic dichroic sheet polarizer including a polyvinyl alcohol-iodine complex. Such a chemical complex is referred to as a chromophore. The base material of an H-type polarizer is a water-soluble, high molecular weight substance, and the resulting film has relatively low moisture and heat resistance and tends to curl, peel or otherwise warp when exposed to ambient atmospheric conditions. In addition, H-type polarizers are inherently unstable, and require protective cladding, layers of cellulose triacetate (TAC), on both sides of the polarizer to prevent degradation of the polarizer in a normal working environment. H-type polarizers are commonly used in liquid crystal displays.